Isothiazolone (ITA) compounds are commonly used as biocides and preservatives in a variety of aqueous and non-aqueous systems, including cooling tower waters, metalworking fluids, deionized water, and personal care products. Metalworking fluids (MWFs) are used to lubricate and cool a workpiece that is being machined. The fluids include water-free oils, and fluids intended to be diluted with water, including soluble oils; semi-synthetic fluids; and synthetic fluids. Aqueous MWFs can support growth of microbes, introducing contaminants such as cells and cell components, along with related byproducts such as endotoxins, exotoxins, and mycotoxins. The ITA-based biocides added to reduce microbial growth have their own hazardous properties, especially dermatitis (skin rash).
There is a need to determine the concentration of the biocide on demand to enable operators of cooling towers, metal working fluids and other aqueous systems to make economical decisions in the field concerning the timing and need for the addition of biocide to their systems The concentration determination needs to be performed rapidly and accurately both in the field and in the lab, without the need for complicated equipment such as HPLC and with minimal sample preparation. In addition, it would be advantageous to have a concentration determination that can be automated to minimize analyst training and enable automated feedback loops (i.e., automated measure and dose).
Attempts have been made to develop a rapid, reliable and sensitive method for determining the concentration of isothiazolones in aqueous systems for use in field applications. These techniques have been less than satisfactory because of the length of time required to complete the analysis, and susceptibility of the techniques to positive and negative interferences caused by additives and ionic impurities commonly found in aqueous systems, and because of the difficulty in obtaining a high degree of sensitivity for measuring low concentrations of isothiazolones. Various additives are typically added to recirculating cooling tower water to prevent or inhibit the precipitation of hardness ions, to disperse scale, and to combat corrosion. For example, polyacrylates, phosphates, phosphonates, iron, zinc, tin and other metals are commonly found in cooling tower water as well as suspended particulate materials such as clay and silt.
U.S. Pat. No. 5,094,957 describes a colorimetric assay for determination of isothiazolone concentration. However, the assay requires hours for color development, and do not reach a minimum value within that time period. Therefore, there remains a need for a method to determine ITA concentration that can be performed in less than 20 minutes, with minimal sample preparation, and is amenable to automation.